Photographic printing process



Patented Dec. 20, 1932 UNITED STATES PATENT OFFICE FRANCIS JOHN SHEPHERD VAND FRANK rons'rnn RENWICK, or LONDON, ENGIiAND,

ASSIGNORS ro ILFOBD LIMITED, or ILFORD, ENGLAND, A BRITISH coMrAmr PHOTOGRAPHIC PRINTING PROCESS No Drawing. Application filed August 29, 1930, Serial No. 478,800, and in Great Britain October 23, 1928;

This invention comprises improvements'in or relating to photographic printing pr'ocand tanning bath which has the property of selectively hardening those portions .of the gelatin which were in immediate contact with the metallic silverof the image, the rest of the gelatin remaining soft. The gelatin is then swelled by immersing the print in warm water; and greasy ink is applied to the surface of the print by means of brushes, gradation being developed by carefully dotting on the ink, which is preferentially taken up by the hardened portions of the gelatin and less readily or not at all by the softer and more swollen portions. The print so obtained may either constitute the final print itself, or may be used as a printer for transn ferring the ink to any desired surface, such as a sheet of paper or the like.

The process described above suffers from the following disadvantages 1. Owingto the fact that the gelatin used 5 in the emulsion must be very water absorbent in character, there is a large percentage of failures due to mechanical defects such as blistering, frilling and breakdown of the emulsion layer. a

2. In order to obtain an optimum swell, ing effect the swelling process which follows the tanning is usually carried out at a temperature well above normal i. e. exceeding 85 F. and the difficulty is that the best temperature is difierent for different types and ages of emulsion and must therefore be separately determined for each case. This procedure of varying the temperature of the bath by trial and error is extremely tedious and unsatisfactory to; carry out in practice.

3. The development of gradation by. dotting ink on to the hardened portions of the gelatin layer by means of a brush takes a very considerable time. Owing to the ink repelling character "and to the softness of the swollen gelatin it is impossible in the usual Bromoil process to apply the ink satlsfactorily by any more speedy method such for instance as by means of a roller;

4. The consistency of the ink employed in the Bromoil process may be varied somewhat to suit the degree of swelling 'of thegelatin but hard rapidly-drying inks are unsuitable by themselves for'the process, so that both hard and soft (slow drying) ,inks are usually employed either in admixture or'in succession with the consequence that a long time, often several days, is required for the ink onthe finished print to dry, whereas harder quicker drying inks are preferred for the improved process described and much delay in the final dying process isthereby avoided.

5. It is necessary in the Bromoil process,

but most difficult, particularly under certain climatic conditions, to keep the print in a suitably damp condition throughout the prolonged inking process. It is the object of the present invention to provide means whereby the above mentioned disadvantages of the Bromoil process hitherto used may be overcome.

The silver-halid'e-gelatin papers. hitherto employed in the Bromoil process havebeen coated with an emulsion containing substantially .no hardening agents, such as-chrome alum etc, in order to ensure that when the print is soaked in warm water immediately before the inking operation, there may be a marked differential swelling between theportions which have been tanned in the bleaching-hardening operation where the silver image previously existed, and the unhardened portions, which were free from image. If the emulsion is too hard the whole area of the print takes up ink much too freely, and a satisfactory picture cannot be obtained. The melting point of the emulsion coating after swelling in water may be taken as a measure of the hardness of the gelatin, and in the Bromoil process as carried out hitherto this melting point has not usually exceeded According to the invention in a photographic printing process of the type described there is employed a silver-halidegelatin emulsion comprising a prehardened gelatin, i. e., a gelatin whose melting point is above 105 F. Preferably the emulsion coniprises a gelatin whose melting point exceeds F. r p

According to a feature of the invention all the operations involving wetting of the printduring its preparation from the unexposed silver-halide-gelatin emulsion up to the completion of the print are carried out at normal temperatures.

-:We have found that further difiiculties arise in practice in printing processes of the Bromoil type particularly when. the image is bleached before fixing, owing to the fact that the bleaching baths employed are ex ceedingly sensitive in their attack on the silver image to variations in the hydrogen ion concentration of the surface of the print upon which they act.

The. developing solutions customarily em ployed in processes of the above type are alkae line in reaction, and very slight local varia tions inalkalinity such as mayarise from irregularities in the thickness of the gelatin layer, or from uneven washing after development, or even from the use of alkaline wash water when fixed bromide prints are washed and dried before bleaching are sufficient to render it certain that the bleaching bath will not have a uniform action over the whole surface of the print, but will attack the silver image to different extents at different points on its surface. This in turn will give rise to local irregularities in the ease with which the ink is taken up by the bleached print, and hence to unevennesses in the appearance of the finished print. It is a further object of this invention to provide means whereby this difficulty may be overcome.

According to a further-feature of the in vention, applicable to thatmodification of a photographic printing process of the type described in which the'bleaching operation vis' carried out before the print is fixed, the

print is brought, prior to bleaching, to a hydrogen ion concentration which is substantially uniform over itswhole surface and comparable with (i 'e. elf-substantially the same order as) that of the bleaching bath to be employed.

According to yet another feature of the invention, the print aft-er development, is transferred to a stop bath. By a stop bath is to be understood a bath which has the effect of stopping the action of a preceding solution with which the print has been treated. Thus a stop bath for use after development normally comprises an acid solution capable of neutralizing the alkaline developer, and thus preventing its further action on the print.

According to a feature of the invention, the stop bath may comprise a solution having a hydrogen ion concentration ranging from 10 to 10- and a buffering action. By buffering action is to be understood the property of maintaining a substantially constant hydrogen ion concentration notwithstanding the addition of small quantities of acids or alkalies to the bath. Thus, for example, a solution of a salt of a weak acid, such for example as sodium acetate acts as a buffer as regards acids. a little hydrochloric acid is added to this solution, thehydrogen ions liberated from the acid will combine with the CH COO- ions liberated from the salts to form moleculesof undissociated acetic acid, and the hydrogen ion concentration of the solution will remain substantially unaltered. By incorporating suitable mixtures of salts therein the solution may be buffered as regards both acids and alkalies.

In a preferred form of the invention the stop bath comprises anaqueous solution'of borax and/or boric acid.

According to a further feature of the in vention,ink is first uniformly applied to the bleached print, preferably after the latter has been dried, by means of a roller or an inkspraying device or the like.

- According to yet another feature of the invention gradation is'developed in theprint by damping the uniformly inked print, and rolling it witha'wet roller of suitable material, e; indie-rubber or felt, which picks up the ink from the non-tanned portions of the gelatin and transfers it preferentially to the tanned portions. The character of the gradation may be controlled locally by light rolling of the damp print with an inky roller which thereby applies more ink to the tanned areas but not to the untanned areas and/or by slightly heavier rolling with a dry clean (uninked) roller of suitable material which will remove any undesired excess of ink.

An example of the method of carrying the invention into practice will now be described.

vA layer of silver-bromide-gelatin emulsion which has been pro-hardened in the course of manufacture by incorporating with it suitable hardening agents, e. g. chrome alum and/or formalin, is exposed to light under a negative, and developed by means of a nontanning developer, such as metol quinol or amidol. 'In the case where amidol is employed the pH number of the developing solution is'of the order of 7.5, whilst in the case of a metol quinol developer the pH number is as high as 9.6. The developed print is then rinsed and transferred to the stop bath, which may be a cold saturated aqueous solution (i. e. an approximately 3% solution) of boric acid. This solution has a pH number of about 5, and has the effect of bringing the surface of theprint to a uniform hydrogen ion concentration Comparable with that of the bleaching bath, which mayconveniently have a pH number of between 4 and 5. The step of treating the print in the stop bath has the further advantage that it enables a bleaching bath of lower ion hydrogen concentration to be used than would otherwise be possible which greatly facilitates the subsequent inking operation.

After removal from the stop bath the print is transferred to a Broinoil bleaching and hardening bath of suitable hydrogen ion concentration (e. g. containing copper-sulphate, chromic acid and potassium bromide), washed well, fixed, washed again, and dried. The dry print is then uniformly inked by means of an ordinary gelatin or other elastic inking roller of the type used in photolithogra-phy. The ink may be any oily, fatty or greasy ink, in which any suitable pigment may be incorporated; or if desired grease crayons may be employed for uniformly colouring the dry print. The print is then damped, either by a brief immersion in cold water or by rolling with a wet fabric-covered roller. Gradation is then developed by rolling the print with a rubberor felt-covered roller, which causes the ink to be picked off the softer portions'of the gelatin and transferred to the tanned portions. If desired further quantities of ink may be applied by means of an ink covered roller or removed by a clean roller so that complete control over the depth of colouring of the print may be obtained. This adjustment of the gradation may be carried out either under the surface of water in a suitable vessel, or on a glass slab or other smooth surface.

By means of the process according to the invention, it is an easy matter to ink a print measuring 12 X 10'' in three to five minutes in full detail and depth of tone, whilst by means of the Bromoil process as hitherto employed, in which soaking in warm water is necessary and inking is effected by means of brushes, it frequently takes from one to two hours to prepare a print of the same size.

The emulsion layers employed in carrying into effect the process according to the invention may be carried on any suitable support such as paper, celluloid, glass, cellulose acetate, cellophane or the like. I

The invention is also applicable to printingprocesses of colour photography accord ing to which two or more coloured images are combined together to give the finished picture either by super-position or by transfer to a common support.

The invention includes a photographic print when made by the special process de scribed herein.

We claim 1. A process of the Bromoil type for obtaining a print in oil pigment'on a HOD-1'6? ticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by the addition of a hardening agent, has been pre-hardened to a degree such'that its melting point is above 105 F., developing the print in a non-tanning developer, selectively harden ng 1n a bleachlng and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver sists in forming the photographic print on a layer of silver-halide-gelatin emulsion which by theiaddition of a hardening agent, has been pre-hardenedto a degree such that its melting point is above 105 F., developing the print in a non-tanning developer, se-

lectivelyhardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, drying the print, applying greasy ink to the surface of the dry I bleached fixed print,'damping the inked print and developing gradation in the damp print by rolling it with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the tannedportions.

3. A process of the Bromoil type for obtaining a print in oil pigment on a. non-re ticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by

the addition of a hardening agent, has been pre-hardene'd to a degree such that its melting point is above F., developing the print in a non-tanning developer, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, applying greasy inkto the surface of the bleached fixed print, and developing gradation in the damp inked print by rolling it inthe cold with a roller-of material which will pick up ink from the non-tanned portions of the gelatin and transfer itpreferentially to the tanned portions.

4. A process of the Bromoil type for obtaininga print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by

I the addition of a hardening agent, has been pro-hardened to a degree such that its melting point is above 105 F.',develop1ng the print in a non-tanning developer, selectively hardening in a bleaching and tanning hath those portions of the gelatin which were in immediate contact with the metallic silver of the image, drying the print, applying greasy ink to the surface of the dry bleached fixed print, damping the inked print and de veloping gradation in the damp print by rolling it in the cold with a roller'of material which will pick up ink from the nontanned portions of the gelatin and transfer it preferentially vto the tanned portions.

5. A process of the Bromoil type for obtaining a print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by the addition of a hardeningagent, has been pro-hardened to a degree such that its melting point is above 105 F, developing the print in a non-tanning developer, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, applying greasy ink to the surface of the bleached fixed print, and developing gradation in the inked print by rollin it under the surface'of cold water in'a suitable vessel with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the-tanned portions.

6. A process ofthe Bromoil type for obtaining a print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which hy the addition of a hardening agent, has been prehardened to a degree such that its melting point is in the region of 160 F, developing the print in 'a non-tanning developer, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with'the metallic silver of the image, applying greasy ink to the surface of the bleached, fixed print and developing gradationin the damp inked print by rolling it with roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the'tanned portions.

7. A process of the Bromoil type for 0h taininga print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion, which by the addition of a hardening agent has been pre-hardened to a degree such that its melting point is in the region of 160 F, developing the print in a non-tanning developer, sclectively hardening in a bleaching and tanningbath those portions of the gelatin which were in immediate contact with the metallic silver of the image, drying the print, apply ing greasy ink to the surface of the dry bleached fixed print, damping the in red print and developing gradation in the damp inked print by rolling witha roller of ma' terial which will pick ink from the nontanned portions of the gelatin and transfer it preferentially to the tannedportions.

8. A process of the, Bromoil type for obtaining a print in oil pigment on a non-reticlated gelatin surface, which consists in forming the photographic print on a layer of silver-halidegelatin emulsion which, by the addition of a hardening agent, has been pre-hardened to' a degree such that its melting point'is in the region of 160 F., d'eve'lop ing the print in a non tanning developer, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, applying greasy ink to the surface of the bleached, fixed print, and developing gradation in the damp inked print by rolling it in the cold with a roller of material which will pick up ink, from the nontanned portions of "the, gelatin and transfer it preferentially tothe tanned portions.

9. A process of the Bromoil type for obtaining a print in oil pigment on a non-reticulated gelatin emulsion surface, which con sists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by the additionof a hardening agent, has been pre-hardened to a degree such thatits melting point is in the region of 160 F.', developing the print in a non-tanning developer, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, drying the print, applying greasy ink to the surface of the dry bleached fixed print, damping the inked print and developing gradation in the damp print by rolling it in the cold with a roller of material which will pick up ink'from the nontann'ed portions vof the gelatin and transfer it preferentially to the tanned portions.

10. A process 'ofthe Bromoil type for obtaining a print in oil pigment on a non-retic ulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which,by the addition of a hardening agent, hasbeen pre hardened to a degrcesuch that its melting point is in the region of 160 F, developing the print in a non-tanning developer, selectively hardening in a bleaching and tanning bath thoseportions of the gelatin which were in imme i'ate contact with the metallic silver of the image, applying greasy ink to the sur: face of the bleached fixed print, and developing gradation in the inked print by rolling it under the surface of cold water in a suitable vessel with a roller of material which will pick up ink from the non-tanned port-ions of the gelatin and transfer it preferentially to the tanned portions.

11. A process of the Bromoil type forobtaining a print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by the addition of a hardening agent has been prehardened to a degree such that its melting point is above 105 F., developing the print in a non-tanning developer, transferring the print to a stop bath having a hydrogen ion concentration ranging from 10- to 10' and a buffering, action, selectively hardeningrin a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, fixing the print, applying greasy ink to the surface of the bleached fixed print and developing gradation in the damp inked print, by rolling it with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the tanned portions.

7 12. A process of the Bromoil type for obtaining a print in oil pigment on a non-reticulated gelatin surface, which consists in forming the photographic print on a layer of silver-halide-gelatin emulsion, which by the addition of a hardening agent has been prehardened to a degree such that its melting point is above 105 F., developing the print in a non-tanning developer, fixing the print, transferring the print to a stop bath having a hydrogen ion concentration ranging from 10" to 10' and a buffering action, selectively hardening in a bleaching and tanning bath those portions of the gelatin in immediate contact with the metallic silver of the image, applying greasy'ink to the surface of the bleached fixed print, and developing gradation in the damp inked print by rolling it with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the tanned portions.

13. A process of the Bromoil type for obtaining a print in oil pigment on a non-reticulated gelatin surface, which 'consists in forming the photographic print on a layer of silver-halide-gelatin emulsion which, by the addition of ahardening agent, has been prehardened to a degree such that its melting point is above 105 F., developing the print in a non-tanning developer, fixing the print, transferring the print to a stop bath having a hydrogen ion concentration varying from 10- to 10 and a bufiering action, selectively hardening in a bleaching and tanning bath those portions of the gelatinwhich were in immediate contact with the metallic silver of the image, drying the print, applying greasy ink to the surface of the print by means of a roller, damping the print, and developing gradation in the damp inked print byrrolling it with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the tanned portions. Y

-14. Aprocess of the Bromoil type for 0htaining a print in oil pigment on a non-reticulated gelatinsurface, which consists in forming the photographic print von a layer of silver 4 halide-gelatin emulsion which, by the addition of a hardening agent, has been prehardened to a degree such that its melting point is above 105 F., developing the print in a nontanning developer, transferring the print to a stop bath having a hydrogen ion concentration varying from 10"? to 10 and a buffering action, selectively hardening in a bleaching and tanning bath those portions of the gelatin which were in immediate contact with the metallic silver of the image, fixing the print, drying the print, applying greasy ink to the surface of the print by means of a roller, damping the print, and developing gradation in the damp inked print by rolling it with a roller of material which will pick up ink from the non-tanned portions of the gelatin and transfer it preferentially to the tanned portions.

In testimony whereof we have signed our names to this specification. 4

FRANCIS JOHN SHEPHERD. FRANK FORSTER RENWIGK. 

